The present invention relates to ion beam apparatus and more particularly, to an ion beam apparatus used for processing a sample and a sample processing method.
As a typical example of a conventional ion beam apparatus using a focusing ion beam, a focusing ion beam processing apparatus described in U.S. Pat. No. 2,765,829 has been known. An outline of the apparatus is illustrated in FIG. 23. Ions discharged from ion generating means 201 are focused on a sample 206 by means of focusing means 202 and illuminating means 203. A restriction diaphragm 204 is adapted to determine a beam diameter. In the apparatus, three modes, that is, A, B and C modes are set in accordance with combinations of lens intensity of the focusing means and illuminating means and individual lens voltages in these modes are stored in lens control means 208 and then used. A difference in irradiation position on the sample 206 between the focusing beams in the modes A, B and C is corrected by means of beam deflecting means 205. In the apparatus, beam diameter and beam current of a focusing ion beam used for processing the sample 206 can be selected but only one focusing ion beam being in or assuming a beam focusing state for maximizing image resolution is used as the ion beam for processing.
Also, as a typical example of a processing method noticing beam distribution of the focusing ion beam, a processing method described in JP-A-2-61954 has been known. In the conventional processing method, beam distribution of a focusing ion beam focused on a target is measured through a knife-edge method and simulation is carried out in accordance with measured data to correct the dosage of ions, so that the processing depth can be stabilized to improve reliability of the processing. The processing speed depends on the beam distribution of the ion beam. Accordingly, irregularity in processing depth attributable to a change in beam distribution due to irregularity in voltage set to an electrostatic lens is taken into consideration in order to make the processing depth constant for every processing operation, thereby improving the yield of processing.
As a typical example of an ion beam apparatus using a shaped ion beam, one may refer to an ion beam processing apparatus described in JP-A-9-186138. An outline of the apparatus is illustrated in FIG. 24. Ions discharged from ion generating means 301 by means of a draw-out electrode 302 are changed in beam divergent angle by means of a beam restriction aperture 303. Lens intensity of focusing means 304 is adjusted such that the focal point of a shaped ion beam 313 coincides with a point near the center of projecting lens 307 and lens intensity of the illuminating means 307 is adjusted such that a mask 306 is projected on a sample 309. A focusing ion beam 312 can be obtained by readjusting the lens intensity of the focusing means 304 such that an intermediate focal point of the focusing ion beam 312 coincides with the mask 306, on the basis of an image of the mask 306 that is projected on the sample 309 as a result of scanning of the ion beam on the mask 306 by means of the beam deflecting means 305 and of scanning of the ion beam on the sample 309 by means of beam deflecting means 308.
In the conventional focusing ion beam processing apparatus, the beam current is ten and several nA at the most and the influence of the skirt spread in ion beam distribution does not matter in practice. For the purpose of improving the throughput, an ion beam of larger current is needed but as the current of the ion beam for processing increases, there arises a problem that the skirt spread in beam distribution increases and dullness of a sectional edge portion in a processing region becomes noticeable to prevent realization of high processing position accuracy.
In the processing method described in JP-A-2-61954, the beam distribution is not changed on the basis of a measurement result of beam distribution, that is, the lens voltage is not changed. Further, beam distribution effective to optimize the shape or form of the sectional edge portion in the processing region in accordance with desired processing is not described clearly. Accordingly, any beam distribution effective to permit the sectional edge portion to be processed sharply cannot be obtained, leading to a failure to realize the optimum processing of the sectional edge portion and the high processing position accuracy. Furthermore, simulation is used and much time is therefore required for calculation, raising a problem that high-speed response control cannot be carried out.
In the conventional ion beam apparatus using a shaped ion beam, the shaped ion beam is used for processing to realize high throughput based on large current while maintaining sectional edge sharpness comparable to or better than that obtained with the focusing ion beam but there arise problems that a focusing ion beam for observation cannot be focused and a difference in position develops between the focusing ion beam for observation and the shaped ion beam for processing. The problem that the observation focusing ion beam cannot be focused, that is, the focusing beam diameter increases upon beam switching is avoided by inserting the beam restriction aperture to change the beam divergent angle. The problem of the position difference between the observation focusing ion beam and the processing shaped ion beam is avoided by making the focal point of the focusing ion beam on a stencil mask and moving the mask so as to correct the position difference between the focusing ion beam and the shaped ion beam for processing. But it is difficult to confirm the setting accuracy of the beam restriction aperture necessary to indicate whether the aperture lies on the optical axis of ion beam optical system, leaving a problem of a position difference between the observation focusing ion beam and processing shaped ion beam attributable to insufficient setting accuracy. Besides, two mechanical drive units for the beam restriction aperture and mask are involved to raise a problem that the position difference between the two beams is aggravated. In addition, two mechanisms of the beam restriction aperture and beam deflecting means are needed as components constituting the apparatus.
As described above, in the conventional ion beam apparatus and ion beam processing method using the focusing ion beam, there arises a problem that the processing position accuracy (inclusive of the sectional edge sharpness) is degraded when the beam current is increased to increase the throughput and conversely, the throughput is degraded when the beam current is decreased to increase the processing position accuracy. In the conventional ion beam apparatus using the shaped ion beam, too, the irradiation positions of the focusing ion beam for observation and the shaped ion beam for processing cannot coincided each other with high accuracy and disadvantageously, high throughput can be attained only at the cost of degradation of the processing position accuracy. Furthermore, disadvantageously, the number of components constituting the apparatus is large.
An object of the present invention is solve the above problems and to provide an ion beam apparatus and a sample processing method which can realize both the high throughput and the high processing position accuracy.
In the present invention, two kinds of ion beams used for processing are prepared of which one is an ion beam being in or assuming a beam focusing state for high resolution of a scanning ion microscope image (hereinafter referred to as SIM image resolution), called hereinafter an ion beam for focusing/processing, and the other is an ion beam for permitting a sectional edge portion in the processing region to be processed sharply, called hereinafter an ion beam for edge processing and the two kinds of ion beams for processing are used intentionally discriminatively in accordance with the beam current to ensure compatibility between the high throughput and the high processing position accuracy.
An ion beam apparatus according to an embodiment of the invention comprises an ion beam optical system including ion generating means for generating ions, focusing means for focusing the ions generated from the ion generating means to form an ion beam, a restriction diaphragm having an opening for restricting current of the ion beam, beam deflecting means for scanning the ion beam on a sample and illuminating means for irradiating the ion beam on the sample, a specimen stage for carrying the sample, secondary particle detecting means for detecting secondary particles generated from the sample under the irradiation of the ion beam, and control means for controlling the ion beam optical system, wherein the control means controls the ion beam optical system such that an ion beam for observation necessary to form a scanning ion microscope image of the sample or an ion beam for processing necessary to process the sample is formed and also controls the ion beam optical system such that when beam current of the ion beam for processing is less than a predetermined value, a focusing/processing ion beam assuming a beam focusing state for high image resolution is formed and when the beam current of the processing ion beam is not less than the predetermined value, an ion beam for edge processing assuming a beam focusing state for permitting a sectional edge portion of the process sample to be processed sharply is formed.
The observation ion beam is rendered to be a small beam current to prevent the sample from being damaged when the sample is scanned with the observation ion beam. Preferably, the control means controls the ion beam optical system such that the edge processing ion beam is formed when the beam current of the sample processing ion beam is not less than a value at which the influence of a skirt of the ion beam becomes noticeable owing to aberration of the ion beam optical system and controls the ion beam optical system such that the focusing/processing ion beam is formed when the beam current is less than that value.
Each of the focusing means and illuminating means includes an electrostatic lens and the control means can perform switching between the focusing/processing ion beam and the edge processing ion beam by switching lens voltage of at least one of the focusing means and illuminating means.
The restriction diaphragm is a restriction aperture having an opening of circular form or a mask having an opening of desired form inclusive of a circle, the opening having an opening area for permitting current of the processing ion beam to have a value not less than the predetermined value.
The restriction diaphragm is a restriction aperture having an opening of circular form and the edge processing ion beam can be an ion beam having a least circle of confusion the position of which substantially coincides with the surface of the sample.
The restriction diaphragm is a mask having an opening of desired form inclusive of a circle, the edge processing ion beam is an ion beam having, at the sample surface position, a sectional form that is analogous to the form of opening of the mask in a direction vertical to the optical axis, and the control means has the function of forming the edge processing ion beam by controlling the lens voltage of electrostatic lens of the focusing means and that of the illuminating means and the function of forming an axis-alignment focusing/processing ion beam for high image resolution by changing the lens voltage of electrostatic lens of the illuminating means on the basis of conditions for formation of the edge processing ion beam.
Preferably, the control means controls the ion beam optical system such that the observation ion beam is formed during sample observation and process region setting and the edge processing ion beam is formed during sample processing.
The control means can include memory means for storing the relation between a value characteristic of the processing ion beam and a control value of the ion beam optical system. The characteristic value of the processing ion beam can be at least one of beam current, beam diameter and beam aperture angle of the processing ion beam.
Preferably, the control means stores, as a difference correction amount, a difference in irradiation position on the sample between the edge processing ion beam and the observation ion beam and has the function of correcting the ion beam irradiation position by using the difference correction amount such that the irradiation position of the edge processing ion beam coincides with that of the observation ion beam on the sample.
An image memory for saving an observation image of the sample observed using the observation ion beam, means for setting a process region at a desired position of the sample by using the observation image saved in the image memory and display means for displaying the set process region and the saved observation image in an overlapping fashion are provided.
Preferably, the restriction diaphragm is a restriction aperture having an opening of circular form and there is provided means for setting a scanning region of the edge processing ion beam by subtracting from the set process region an amount corresponding to a precedently determined beam radius of the edge processing ion beam when the edge processing ion beam is an ion beam having a least circle of confusion the position of which substantially coincides with the sample surface.
Preferably, display means for indicating whether the ion beam now irradiated on the sample is the observation ion beam or the processing ion beam and display means for indicating, when the ion beam now irradiated on the sample is the processing ion beam, whether the processing ion beam is the focusing/processing ion beam or the edge processing ion beam.
Preferably, when the restriction diaphragm is a mask including an opening of desired form and the edge processing ion beam is a shaped ion beam, an image memory for saving an observation image of the sample observed using the observation ion beam, means for displaying a position of the optical axis of the edge processing ion beam and a region referenced to the optical axis and scheduled to be processed by projecting the edge processing ion beam upon the sample in a fashion of overlapping with the saved observation image, and means for setting the process region by designating the position of optical axis of the edge processing ion beam such that the region scheduled for processing coincides with a desired position.
An ion beam apparatus according to another embodiment of the invention comprises, in addition to the aforementioned components, transport means for transferring an extractive sample obtained by separating part of the sample to a position different from an extractive position and an extractive sample stage for carrying the extractive sample transferred by the transport means. The control means includes desired form processing control means for processing the form of the extractive sample into a desired form including at least one of elongated lamina, rectangular prism, triangular prism and gear.
A deposition gas source for supplying a raw material gas for formation of a deposition film in the ion beam irradiation region on the sample is provided, and the control means may include beam adjusting means for forming an edge deposition processing ion beam assuming a beam focusing state similar to that of the edge processing ion beam.
The ion beam apparatus may comprise at least one upper intermediate focusing means for focusing the ion beam between the focusing means and the restriction diaphragm. At least one lower intermediate focusing means for focusing the ion beam may be interposed between the restriction diaphragm and the illuminating means.
The control means may include brightness change detecting means for detecting a change in brightness of an ion microscope image observed during processing and end point detecting means for stopping the processing at the time that the brightness change is detected.
Preferably, there is provided output gain adjusting means for adjusting the output gain of the secondary particle detecting means in accordance with the magnitude of beam current of the processing ion beam. By providing the output gain adjusting means, brightness saturation of the SIM image can be prevented.
A plurality of ion beam optical systems may be provided in which optical axes of at least two ion beam optical systems cross each other at one point. Exemplarily, an ion beam optical system for forming only the edge processing ion beam and an ion beam optical system for forming the observation ion beam and the focusing/processing ion beam may be provided.
A sample processing method according to an embodiment of the invention, adapted to process a sample by irradiating ions generated from ion generating means through an ion beam optical system, comprises the steps of performing processing by conditioning the ion beam optical system such that an image of the ion generating means is formed sharply on the sample when ion beam current is less than a predetermined value, and performing processing by conditioning the ion beam optical system such that the position of a least circle of confusion of the ion beam substantially coincides with the sample surface when the ion beam current is not less than the predetermined value.
A sample processing method according to another embodiment of the invention, adapted to process a sample by irradiating ions generated from ion generating means through an ion beam optical system including a mask having an opening of desired form, comprises the steps of performing processing by conditioning the ion beam optical system such that an image of the ion generating means is formed sharply on the sample when ion beam current is less than a predetermined value, and performing processing by conditioning the ion beam optical system such that an image of opening of the mask is formed sharply on the sample when the ion beam current is not less than the predetermined value.